Method of producing a molded commutator

ABSTRACT

A flanged cylindrical body formed by suitable means is disposed in a cavity die assembly and then a plurality of commutator bar dividing grooves and commutator riser dividing grooves are formed in the flanged cylindrical body rectilinarly by a suitable stamping operation, without resorting to mechanical cutting at all, while taking the flow balance of the material into consideration, thereby to form a shrink ring for the commutator. Thereafter, a molding material is charged into the thus formed shrink ring for the commutator and the material connecting the commutator bars and commutator rises is removed, whereby a molded commutator is produced.

United States Patent [191 Ohuchi et al.

METHOD OF PRODUCING A MOLDED COMMUTATOR Inventors: Yasushi Ohuchi; Hisanobu Kanamaru; Teruhisa Honshlma, all of Hitachi, Japan Assignee: Hitachi, Ltd., Tokyo, Japan Filed: June 5, 1970 Appl. No.: 43,788

[30] Foreign Application Priority Data June 13, 1969 Japan ..44/47l75 References Cited UNITED STATES PATENTS Reisnecker ..29/597 [451 I Jan. 9, 1973 3,407,491 10/1968 Clevenger et a1 ..29/597 3,478,421 11/1969 Preece 3,482,307 12/1969- Yamaguchi ..29/597 Primary Examiner-Richard J. Herbst Assistant Examiner-Carl E. Hall Attorney-Craig, Antonelli and Hill [57] ABSTRACT A flanged cylindrical body formed by suitable means is disposed in a cavity die assembly and then a' plurality of commutator bar dividing grooves and commutator riser dividing grooves are formed in the flanged cylindrical body rectilinarly by a suitable stamping operation, without resorting to mechanical cutting at all, while taking the flow balance of the material into consideration, thereby to form a shrink ring for the commutator. Thereafter, a molding material is charged into the thus formed shrink ring for the commutator and the material connecting the commutator bars and commutator rises is removed, whereby a molded commutator is produced.

3 Claims, 18 Drawing Figures PATENTEDJAH ems 3,708,872

SHEET 3 0F 4 INVENTORS \IASUSHI oaucm, Husmobu KANAMARU AND TERUHISA HONSHIMA cm nnroqem, smart Hal! ATTORNEYS METHOD OF PRODUCING A MOLDED COMMUTATOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of producing a molded commutator.

2. Description of the Prior Art In the production of a commutator by a molding method, it is usual to form the commutation bars from a copper pipe by a mechanical cutting operation such as broaching. In this method, however, cutting of a blank copper pipe in the first step of the operation must be effected by using a saw so as to avoid any deformation of the pipe. In addition, the formation of the commutator risers by cutting riser dividing grooves by means of a cutter is usually effected after the commutator bars have been formed by broaching because the commutator risers and the commutator bars cannot be formed concurrently by machining.

In this case, since machining of the shrink ring of the commutator is carried out before charging a molding material, a step of removing the chip is inevitable. Therefore, the conventional method as described above not only provides the danger of shorting between the commutator bars through the chip, but also requires a high skill in machining the commutator bar dividing grooves and the commutator riser dividing grooves which must be in alignment with each other, as these grooves cannot be machined concurrently, and hence this is not adapted for the mass production of commutators. A further disadvantage of the conventional method which cannot be overlooked, is that a large quantity of copper material is wastefully consumed because in the formation of the commutator bars independently of each other, the portion connecting the commutator bars must be cut away by a lathe after charging the molding material.

SUMMARY OF THE INVENTION An object of the present invention is to provide a shrink ring for a commutator having commutator bar dividing grooves and commutator riser dividing grooves formed therein, from a relatively small quantity of material and in a relatively small number of operational steps by a cold forging method, without involving a mechanical cutting operation.

Another object of the invention is to provide a method by which a groove to be formed in each side surface of a commutator bar for the purpose of producing a stronger bond with a molding material can be formed concurrently with the formation of a shrink ring of commutator, without resorting to a mechanical cutting operation.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate an embodiment of the molded commutator producing method according to the present invention.

FIG. 1 is a sectional view illustrating the step of working the starting material.

FIG. 2 is a sectional view illustrating the step forming an annular body.

FIGS. 3 and 4 are sectional views illustrating the step of forming a flanged cylindrical body.

FIG. 5 is a sectional view illustratingthe first groove cutting step using a stamping die.

FIG. 6 is a sectional view taken on the line VIVI of FIG. 5. Y

FIG. 7 is a sectional view illustrating the dividing groove forming step.

FIG. 8 is a sectional view taken on the line VIII-VIII of FIG. 7.

FIG. 9 is an enlarged fragmentary sectional view showing the essential portion of FIG. 8.

FIG. 10 is a sectional view taken on the line X-X of FIG. 8.

FIG. 1 1 is an enlarged fragmentary sectional view showing the essential portion of FIG. 10.

FIG. 12 is a perspective view of a shrink ring for a commutator.

FIG. 13 is an enlarged fragmentary side view of FIG. 12.

FIG. 14 is a sectional view illustrating the molding material charging step.

FIG. 15 is a perspective view of the commutator obtained from the step of FIG. 14.

FIG. 16 is a sectional view illustrating the step of forming coil mounting grooves in the commutator risers.

FIG. 17 is a perspective view of the commutator obtained from the step of FIG. 16.

FIG. 18 is a perspective view of the complete molded commutator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a method of producing a molded commutator in which, as shown in FIG. 18, commutator bars If each having an armature coil mounting notch 33 formed in the riser portion are arranged in concentrical relation and molded by a molding material. In describing the production process, a copper rod is first of all cut into a piece of suitable length to provide a starting material 1. This starting material 1 is disposed in a cavity die assembly 2, 3 and pressed by a stamping die 4 to obtain a disc-shaped body 10. The disc-shaped body thus obtained is then disposed in a cavity die assembly 5, 6 in the second step (FIG. 2) and deformed by a punch 7 into the shape of a cup having a bottom wall 1b and a cylindrical side wall 10.

After the second step, the cup-shaped body is transferred to apparatus for performing the third step (FIG. 3), wherein it is mounted on the upper surface of a cavity die assembly 8, 9, l0 and the material of the bottom wall 1b thereof is caused to flow radially outwardly by a punch 13 to form an annular flange 1d, while confining the outer diameter of the cylindrical side wall 10 by means of a core die 11 and the height of the same by a core die 12. Then, the body obtained from the third step is transferred onto a die 14 of FIG. 4 and the bottom wall lb is punched by a punch 16, while confining the outer peripheral surface thereof by a core die 15, to form a flanged cylindrical body 17.

In the fifth step (FIG. 5), grooves 1e are formed in the inner peripheral edge portion at the same pitch as the commutator bar dividing grooves to be formed in the next step, as shown in FIG. 6. The next step is the one of forming grooves 18 and 19 which will divide the commutator bars If and the commutator risers 1g. Namely, as shown in FIG. 7, the flanged cylindrical body 17 is inserted in an inverted position into a cavity die 21 having a die 20 provided therebeneath, and the grooves are formed by pressing by the cooperation of a punch 22 and a stamping die 23, while defining the inner diameter of the body by said punch 22. Here, the punch 22 and the stamping die 23 are respectively provided with circumferentially equally spaced working teeth 22a, 23a at the lower portions thereof. These working teeth are formed in opposed relation to grooves 21a, 21b formed in the core die 21 respectively with a slight space therebetween, and are provided with projecting teeth 23c for forming grooves 18a in the side surfaces of the commutator bars concurrently. In the die 20, the working teeth 22a and the grooves 20a are in close contact with each other. In this step, therefore, the flanged cylindrical body 17 obtained in the fourth step (FIG. 4) is deformed by the cavity die 21, the working teeth 22a of the punch 22 and the working teeth 23b of the stamping die 23, and the excess material li is extruded in the same configuration as the working teeth 22a. Thus, a shrink ring for a commutator as shown in FIG. 12 is formed.

In the sixth step (FIG. 14), a bush 30 is inserted into the hollow of the commutator shrink ring, obtained in the preceding step, by way of a core pin 29, while holding the outer peripheral surface of the ring by a cavity die assembly 24, 25, 26, 27, 28, and then a molding material 31 is charged with pressure into the gaps formed between said bush and the shrink ring, whereby a molded commutator ring as shown in FIG. is obtained. In the eighth step (FIG. 16), armature coil mounting notches 33 are formed by punching tool 34 while holding immovably the peripheral wall of the ring by a die 32. While it is usual to punch the armature coil mounting notches 33 after the molding, these notches may be formed before the molding, if it is possible to prevent deformation of the risers 1g. In the final step, the material connecting the adjacent commutator bars lfand adjacent risers 1g with each other is cut away by means of a lathe, whereby a complete molded commutator is obtained. The fifth step (FIG. 5) is provided for the purpose of precluding the formation of a burr in the gap at the joint of the individual pieces of the stamping die assembly. Therefore, this step can be eliminated if it is technically possible to form the stamping die as a unitary piece.

It is added that the flanged cylindrical body obtained from the fourth step in not necessarily produced by the process described herein but can be produced from a pipe or directly by die casting without going through a plurality of steps.

In forming the commutator ring in the fifth step, the work is performed while holding the end faces of the commutator bars by the die and, therefore, a burr will not be formed at the end faces by stamping. This eliminates an additional mechanical work conducted for the purpose of preventing the electrical shorting between the adjacent commutator bars 1f. In addition, according to the present invention the holding grooves 18a are formed in the side surfaces of the commutator bars concurrently when the commutator bar dividing grooves 18 are formed and, therefore, an additional step of forming such grooves can be eliminated. Thus,

by practicing the method of this invention, a molded commutator can be produced in a rational manner with an excellent productivity in a relatively less number of operational steps.

As will be understood from the foregoing description, according to the present invention it is possible, by employing a cold forging method in the formation of a shrink ring for a commutator, to prevent the electrical shorting of the commutator bars through a chip being produced in the working stage, and to provide a molded commutator which requires a substantially less quantity of copper material and which is inexpensive and highly productive.

We claim:

1. A method of producing a molded commutator having a plurality of commutator bars and a plurality of commutator risers comprising the steps of:

a. forming a cylindrical body with a flange portion at one end thereof,

b. forming a plurality of commutator bar dividing grooves longitudinally extending in an inner wall of said cylindrical body and a plurality of commutator riser dividing grooves connected to said commutator bar dividing grooves respectively and radially extending in a circular wall of said flange portion by forcing a punch, which has working teeth adapted to form said commutator bar dividing grooves, inside said cylindrical body and simultaneously pressing a stamping die, which has working teeth adapted to form said commutator riser dividing grooves, onto said circular wall of said flange portion, while steadily fixing the position of the end face of the other end of said cylindrical body and the position of the outer wall of the same, thereby producing a cylindrical shrink ring of a commutator having elements including said commutator bars and said commutator risers con nected thereto, said elements being connected to one another by a part of said cylindrical body with said flange portion,

c. filling a molding material into said cylindrical shrink ring and into said commutator riser dividing grooves,

of said commutator risers, and

e. removing said connected portion of said elements from said shrink ring, thereby isolating said elements from each other.

2. A method of producing a molded commutator as defined in claim 1, further comprising the step of, prior to the forming of said commutator bar dividing grooves and said commutator riser dividing grooves, forming preliminary radial grooves in said circular wall of said flange portion at the same pitch as that of said commutator bar dividing grooves so as to prevent an accumulation of burrs in a gap between said punch and said stamping die.

3. A method of producing a molded commutator as defined in claim 1, wherein said commutator bar dividing grooves are formed so as to provide a longitudinally extended groove in each of both side walls of each of said commutator bars, thereby strengthening the coherence between said commutator bars and the molded body of said molding material filled into said cylindrical shrink ring.

. forming an armature coil mounting notch in each 

1. A method of producing a molded commutator having a plurality of commutator bars and a plurality of commutator risers comprising the steps of: a. forming a cylindrical body with a flange portion at one end thereof, b. forming a plurality of commutator bar dividing grooves longitudinally extending in an inner wall of said cylindrical body and a plurality of commutator riser dividing grooves connected to said commutator bar dividing grooves respectively and radially extending in a circular wall of said flange portion by forcing a punch, which has working teeth adapted to form said commutator bar dividing grooves, inside said cylindrical body and simultaneously pressing a stampiNg die, which has working teeth adapted to form said commutator riser dividing grooves, onto said circular wall of said flange portion, while steadily fixing the position of the end face of the other end of said cylindrical body and the position of the outer wall of the same, thereby producing a cylindrical shrink ring of a commutator having elements including said commutator bars and said commutator risers connected thereto, said elements being connected to one another by a part of said cylindrical body with said flange portion, c. filling a molding material into said cylindrical shrink ring and into said commutator riser dividing grooves, d. forming an armature coil mounting notch in each of said commutator risers, and e. removing said connected portion of said elements from said shrink ring, thereby isolating said elements from each other.
 2. A method of producing a molded commutator as defined in claim 1, further comprising the step of, prior to the forming of said commutator bar dividing grooves and said commutator riser dividing grooves, forming preliminary radial grooves in said circular wall of said flange portion at the same pitch as that of said commutator bar dividing grooves so as to prevent an accumulation of burrs in a gap between said punch and said stamping die.
 3. A method of producing a molded commutator as defined in claim 1, wherein said commutator bar dividing grooves are formed so as to provide a longitudinally extended groove in each of both side walls of each of said commutator bars, thereby strengthening the coherence between said commutator bars and the molded body of said molding material filled into said cylindrical shrink ring. 